This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. The catabolite activator protein (CAP;also known as the cAMP receptor protein, CRP) activates transcription at more than one hundred promoters in Escherichia coli. CAP, a 45 kDa homodimer, binds to specific DNA sites in or near target promoters and enhances the ability of the 450 kDa E. coli RNA polymerase holoenzyme (RNAP) to bind and initiate transcription. Simple CAP-dependent promoters--i.e. promoters that require only CAP for transcription activation--can be grouped into two classes based on the position of the DNA site for CAP and the corresponding mechanism for transcription activation. To complete our understanding of how CAP accomplishes transcription activation, full structural models for CAP-holoRNAP-DNA promoter complexes are required.